Up to 2,000 women in business and finance have gathered to call for more action to stop gender inequality in the City and across the British economy as a whole.

The conference came as a new poll showed that 79% of London-based female professionals said men and women were treated differently in the workplace.

"There is gender asbestos – it's in the walls and it will take a bit of time and more work to get it out," said Avivah Wittenberg-Cox, chief executive of 20-first, a Paris-based gender consultancy.

Just over half of women questioned believe their firm is committed to ensuring gender equality, but only a third say management has made any improvements in addressing the issue over the past five years, according to a YouGov survey of 610 women commissioned by Deutsche Bank.

"There is fatigue around this issue: we've been talking about it for years and still nothing is happening, and women know it," said one woman at the event at the Barbican centre.

Only 10% of directors in Britain's top 100 companies are women, and 25 of the top firms have no women board members at all. This was despite the fact that women represent about 60% of university graduates in Europe, and made about 80% of household purchasing decisions – including ones about cars, computers, property, holidays and telephones, Wittenberg-Cox said.

The women questioned in the poll said business had to be made more meritocratic, but without positive discrimination rules to increase the number of women at the board level. At present, men and women are sharing entrance positions into the labour market on a 50-50% basis, but the representation of females in leadership positions plunges to 20%.

Men held the key to change, as they still controlled Britain's top positions, Wittenberg-Cox said. "We need to stop men sending women to assertiveness courses so they will sound more like them," she said. "We need to stop fixing women, we don't need any fixing."

Women should also assess their situation, and move on if their company was blocking their way. "You think it's them, and not me, and then have the courage to leave," said Heidi Mottram, chief executive of Northumbrian Water, who moved out of a company after saying she got "stuck".